(a) Technical Field
The present disclosure relates to a device for indirectly cooling a battery module of an eco-friendly vehicle, and more particularly, to a device for indirectly cooling a battery module of an eco-friendly vehicle, that indirectly cools the battery module using an interfacial plate into which a heat pipe is inserted, to maximize battery heat emission performance and simultaneously, prevent degradation of battery performance.
(b) Background Art
Eco-friendly vehicles refer to electric vehicles, fuel-cell vehicles, or the like which generate no emissions, and in the eco-friendly vehicles, batteries are mounted to drive motors for driving a vehicle. Since the reliability and stability of a battery system serve as important factors for determining the productivity of electric vehicles, the battery system should be maintained at a proper temperature range of about 35° C.-40° C. to prevent battery performance from degrading due to change in various external temperatures. Thus, a need exists for a heat control system for a pouch cell module exhibiting improved heat emission performance in a general climate condition and that maintains a proper temperature of a battery in a low-temperature environment.
For a battery of an electric vehicle, a local temperature difference may be generated between battery cells due to heat generated by fast charging, high power, the number of times of repetitive charging, or the like, or a thermal runaway may occur which deteriorates the battery's efficiency and stability. These phenomena are known as occurring since heat emission or heat diffusion to the outside the battery is insufficient when compared to heat generated inside the battery.
A pouch-type battery cell undergoes a change in volume due to intercalation and deintercalation of lithium ions into electrode materials during charging and discharging, causing potential damage in a separator between two electrode materials as well as expansion of electrodes in the battery. The damage in the separator causes battery performance degradation and battery final capacity reduction as well as internal resistance generation, and thus, a heat-emission interfacial material for coping with battery volume expansion is required.
When the pouch-type battery expands significantly, a polymer pouch may be damaged and thus internal electrolyte may leak and gas may be discharged. Since a pouch-type cell module is configured by stacking several cells, when expansion or gas emission or explosion occurs, direct damage may occur to neighboring cells. Expansion of the pouch-type battery may accelerate heat emission by reducing the size of a cooling air flow path for cooling between battery cells.
Moreover, as an example of conventional techniques, a direct cooling scheme is widely known in which a cooling air directly contacts the surface of the battery to emit heat generated in the battery. In particular, the cooling air directly cools the battery and thus thermal conductivity of a housing material that encloses the battery may be omitted; but a cooling air flow path in which the cooling air flows should be secured in a predetermined size or larger between battery cells, thus limiting an increase in the number of cells inserted per unit volume.
A known conventional technique discloses a battery heat emission structure using a heat pipe in which a battery heat emission feature may be improved by forming an indirect cooling structure in which the heat pipe of a flat panel type is inserted between lithium ion batteries and heat emission pins in the form of louvered fins, which are condensations, intersect each other in an upper portion of the heat pipe. However, such a technique may not handle volume expansion of a battery (e.g., a pouch-type battery) due to fast charging/discharging.
Generally, the surface of the pouch-type battery is not even, and thus, when the heat pipe of a flat panel type disclosed in the conventional techniques is placed between the battery cells, an interfacial delivery resistance may be generated due to degradation of flatness between the flat panel type heat pipe and the battery cell. In addition, a flat panel type heat pipe applied in another embodiment of the conventional examples directly contacts the surface of the battery, causing a potential tear in the pouch type battery by metallic burr generated in heat pipe manufacturing during vehicle's vibration or battery module assembly.
Moreover, another disadvantage of a conventional battery module is that a material or a device is not provided to cope with cold start of the vehicle or power degradation in a low-temperature environment. In other words, as illustrated in FIG. 1, a general lithium ion battery may cause vehicle power performance degradation in a low-temperature environment, and more specifically, power performance may begin to be degraded from about 10° C. or lower, such that a performance degradation of about 30% is degraded at about −20° C. Therefore, a separate material or device is needed which may heat the battery to about 30° C.-40° C. in a cold start and low-temperature environment.